Various methods for producing tablets are known in the art. Widely used methods comprise starting materials in powder form, such as the active agent and one or more additive. The starting materials are blended, and the obtained blend is compressed in a die between the moving punches of a tablet press, yielding a tablet. Other methods are based on a sequence of melting and solidification rather than compression. In these methods thermoplastic polymers serve as binders in the final tablet. For the preparation of the tablets, the starting materials, including the thermoplastic binders, the active agents and optionally further additives are blended, heated in an extruder to melt into a homogenous extrudate. The extrudate can be further processed to obtain the desired shape and size of the tablet, for example by directly introducing the extrudate in a cavity of appropriate shape (injection molding). Alternatively, the extrudate can be expelled from the extruder and be shaped using calendars, die cutter, and the like.
A disadvantage of methods requiring the shaping of an extrudate lies in the fact, that the shaping step leaves marks on the finished tablets. After calendering, for example, the tablets may be connected by so-called flash (also referred as burrs) after separation. Even after separating the tablets by additional processes such as cutting the flash, it is difficult to completely remove them. Likewise, tablets formed by injection molding usually also have flash due to the fact that for release of the tablets the injection molding cavity must be opened. For that reason, the wall of the molding cavity is usually formed by two or more partial walls, which form a closed cavity during the shaping step, and are removed to release the shaped tablet. Since it is difficult to create a perfectly smooth surface in the regions, where the partial wall contact each other during the injection molding, extrudate can also enter those regions, leading to flash or at least visible ridges (“burrs”) on the surface of the finished tablet. Flash or ridges, however, are aesthetically inacceptable, and might modify the release profile of the active agents, e.g. by altering the surface area or shape of the tablet. In case the tablet is to be swallowed by a higher organism, flash or ridges might even be hazardous by injuring mouth cavities or esophagus or otherwise interfering with swallowing the tablet.
Consequently, the flash (e.g., burrs) have to be removed. Present methods comprise cutting off the flash, or reducing their volume by polishing the surface of the tablets by methods such as tumbling. However, cutting or tumbling may not be effective to completely remove disturbing flash or ridges, but rather leaves remnants thereof, often visible as rough spots, on the surface. Moreover, in the case of tablets made from impact resistant materials, tumbling is ineffective. It is possible to cool down the tablets to temperatures, where the tablet material becomes brittle enough to allow flash removal by tumbling. However, performing the tumbling procedure at low temperature increases the danger of moisture condensation on the surface of the tablets, which may affect the shape of the tablet, cause decomposition of the ingredients or affect the shelf life of the tablet. As such effects are not acceptable, tumbling at low temperatures requires a strict control of ambient moisture, thus rendering the production of the tablets more difficult and more expensive. Therefore, there is a need for a method for obtaining tablets having acceptably even tablet surfaces.